This invention relates to an acceleration detector and, more particularly, to an acceleration detector for detecting knocking of an internal combustion engine.
A conventional acceleration detector for detecting knocking of an internal combustion engine comprises a housing adapted to be rigidly secured to an engine and an acceleration transducer assembly disposed within the housing for detecting the acceleration on the housing which represents knocking of the engine. The housing comprises a base and a cover securely connected together. The transducer assembly comprises a disc diaphragm and a piezoelectric element attached to the center of the diaphragm for sensing flexure thereof for generating a signal representative of the acceleration of the housing. The diaphragm is rigidly supported by the housing at its outer continuous circumferences edge portion. Typically, the circumference edge portion is firmly clamped between edges of the base and the cover of the housing which are mechanically connected together by means of caulking.
The sensitivity of the acceleration transducer assembly comprising the diaphragm and the piezoelectric element is at its best at the resonance frequency f.sub.0 which is determined by the diameter and the thickness of the diaphragm and the piezoelectric element, whereupon the output from the transducer assembly is at its maximum. The resonance frequency f.sub.0 is an important characteristic of the acceleration detector and it is required that the deviation of the resonance frequency f.sub.0 from one detector to another is minimized.
Another important factor affecting the resonance frequency f.sub.0 is temperature as illustrated in the graph of FIG. 5. Since the temperature characteristics of the acceleration detector determine changes in the resonance frequency f.sub.0 due to the temperature change, and this change in the resonance frequency f.sub.0 affects the system performance, it is desirable to reduce the amount of the above change.
With the conventional acceleration detector as described above, the disc-shaped diaphragm is rididly supported by the housing at its entire circumferential edge, so that the temperature characteristics of the resonance frequency are poor and it is desired to improve the temperature characteristics of the resonance frequency of the acceleration detector.